I am impressed. Just run the editor from source with my sample docx for generating a new epub. Works very well
Can you do the same behavior for an existing epub for updating? E.g if you are looking for the file I gave you (FonttestwithoutembededFont.epub). If you embed the font it find the regular one and for the light version it found 2 possible matches based on weight. But only one is correct because there is only one as light regular. The other one is light italic and that one isn't used for this epub. Guess, if you are able to get that in line too, most users are happy with the new solution.
Best regards,
DD